The invention concerns a method for heating a lubricating system of rotating or oscillating components, in particular for a combustion engine or a transmission, comprising at least one oil suction tube which is disposed inside an oil sump, and a bypass line which bypasses the oil return line, wherein a valve is disposed in the bypass line.
DE 27 53 716 concerns a heating device emitting hot air designed for motor vehicles powered by a combustion engine, comprising a heat exchanger which can be supplied with atmospheric air to transfer heat to a heat transfer medium flowing inside a pipe circuit, said pipe circuit having also a heat exchanger connected therein that absorbs exhaust gas heat from the combustion engine and transfers it to the heat transfer medium. The pipe circuit for the heat exchanger of the heating device is in heat-transferring connection with at least the lubricating oil circuit of the combustion engine. In this instance a heat transfer to the lubricating oil in a dry sump container is achieved in that the heat from a heat transfer medium flowing in a flow line is transferred to the lubricating oil in the dry sump container.
GB 2 381 576 A discloses an exhaust gas heat recovery device comprising a heat exchanger line and a bypass line. A heat exchanger is disposed in the vicinity of the heat exchanger line. At least one valve assembly is provided in the heat exchanger line and/or in the bypass line to influence the exhaust gas flow amount in the heat exchanger line. When installed, at least the heat exchanger line has a fall in an exhaust gas flow direction.
EP 0 885 758 B1 concerns a method for the operation of a heat exchanger in the exhaust gas flow of a combustion engine for motor vehicles, in which the exhaust gas flow can be split into a main line and a bypass line. The heat exchanger is disposed in the bypass line. In the warm-up phase, a back-pressure can be created in the main line, which causes a counter-pressure at the exhaust discharge port of the combustion engine. The warm-up phase is split into two phases, wherein in the first phase a higher counter-pressure is generated than in the second phase. A first valve is disposed in the main line between the bypass line connections, wherein a second valve is disposed in the bypass line downstream of the heat exchanger. Both valves are closed in the first phase, and in the second phase the first valve is closed but the second valve is open.
EP 0 202 344 describes an articulated tanker truck for the transport of liquid goods, wherein a medium flowing along the outside of the tank transfers heat to the contents of the tank. The medium is a heat transfer oil that flows in the circuit through at least one heat exchanger, which is heated by the hot exhaust gases of the combustion engine of the articulated tanker truck. To reduce the toxic content of the exhaust gases a catalytic converter, through which the combustion gases flow, is deposed upstream of the heat exchanger.
DE 199 08 088 A1 refers to a combustion engine, in particular a Diesel combustion engine, for a motor vehicle, comprising a passenger room heating device, an exhaust line, a coolant line, which forms a cooling circuit together with a first pump, to which the combustion engine is connected, and an exhaust gas heat exchanger for transferring exhaust heat to a heating heat exchanger. The exhaust gas heat exchanger operates between the exhaust line and a line for the circulation medium, which forms a circulation circuit to which the heating heat exchanger is directly or indirectly connected.
However, DE 199 08 088 A1 also refers to a combustion engine, in particular a Diesel combustion engine, wherein the combustion engine is connected to a first bypass that branches off from the coolant line, wherein a first thermostat valve is disposed in said first bypass, which largely closes said bypass until a median coolant temperature is reached, and which opens above said coolant temperature. In a second bypass, which extends parallel to the first bypass, a second thermostat valve is disposed, which largely closes said second bypass above the median cooling [sic] temperature.
DE 100 47 810 A1 concerns a heating circuit with an auxiliary heating device for motor vehicles with a combustion engine, which is part of a separate bypass circuit that can be switched into the heating circuit via a changeover device. The exhaust system of the vehicle's engine is used as an auxiliary heating device, from which the exhaust gas heat is transferred to the heating circuit. If the heat requirement of the passenger room heating device fails to meet the exhaust heat supply, the exhaust heat supply can be increased by means of the engine. Nevertheless, DE 100 47 810 A1 also refers to a process for operating a heating circuit with an auxiliary heating device for motor vehicles with a combustion engine, which is designed as an exhaust gas heat exchanger through which the engine exhaust gas and the coolant flow. The engine operating parameters can be adjusted to increase the heating performance of the auxiliary heating device.
EP 1 094 214 A2 refers to a heat recovery device comprising a circulation line in which a heat transfer medium circulates through an engine cooling unit, and an exhaust heat exchanger to utilise an engine's exhaust gases, and a line that connects a discharge side of the circulation line with an discharge port of the heat exchanger. The exhaust heat exchanger is disposed transversely through the circulation line on a side upstream of the engine cooling unit. The heat transfer medium introduced into the exhaust heat exchanger is adjusted to a lower temperature that is sufficient to lower the temperature of the water vapour contained in the exhaust gas stream from which heat is transferred to the heat transfer medium to lower its dew point.
When conducting an NEDC test (New European Driving Cycle) on a combustion engine in its cold state (starting temperature approx. 24° C.) the fuel consumption is approximately 10 to 15% higher than in the same test in which the engine oil temperature is approximately 90° C. when starting, which is the so-called NEDC hot test. The reason for this is, amongst others, that the lubricating oil has a higher viscosity at lower temperatures, and that the fuel condenses on the cylinder walls and finds its way into the engine oil. Moreover, measures are introduced to heat up the catalytic converter more quickly, for example though retarding the ignition, raising the idle speed and enrichment through secondary air injection. Furthermore, the majority of the exhaust emissions occur during the cold start phase of the combustion engine when the catalytic converter has not yet reached the required operating temperature. At the same time the majority of the energy supplied is discharged unused as exhaust gas enthalpy. This makes up in total approximately 30 to 40% of the energy of the supplied fuel.
It is known to improve the warm-up phase of the engine by employing exhaust heat exchangers that use a complex way of heating up the engine oil and reducing the oil pressure. On the other hand, this poses the problem of how to protect the engine, and in particular the engine oil, from overheating in this heating process. This is the reason why additional high capacity oil coolers are used. The known solutions are very elaborate and result only in a small reduction in the fuel consumption, hence a practical implementation hardly ever takes place for economic reasons.
FR 2 896 531 A1 discloses a method for speeding up the heating of a lubrication system of rotating components for a combustion engine. It comprises an oil suction tube disposed in an oil sump as well as a bypass line that bypasses the oil return lines. A valve is disposed in the oil bypass line with which the bypass line and/or at least one of the oil return lines can be connected to the suction pipe of an oil pump and the pressure line of a lubricating system. The routing chosen for the oil bypass line is not advantageous for raising the temperature more quickly.
It is desirable to improve a combustion engine or a transmission, in particular an automatic transmission of the kind described at the beginning using simple means so that the engine oil is heated up more quickly to reach the operating temperature in the cold-start phase or the warm-up phase respectively to achieve not only reduced fuel consumption but also a reduced emission of pollutants, wherein overheating of the engine oil is supposed to be prevented.
According to an aspect of the invention, an oil bypass line, which bypasses the oil return line, is connected to the suction line of an oil pump and to the pressure line of a lubricating system, wherein the oil bypass line, in the instance of a combustion engine, preferably extends through at least one cylinder head and/or one cylinder block and/or at least one turbo charger, and in the instance of a transmission, it preferably extends through at least one heat exchanger of the combustion engine and/or through at least one heating rod. Moreover, when dropping below a certain temperature limit and when exceeding a certain minimum pressure of the lubricating oil, in the pressure line of the lubricating system a bypass valve in the oil bypass line is at least partially opened so that a partial flow of the lubricating oil does not flow through the oil sump during a warm-up phase of the lubricating system until either the minimum pressure or the temperature limit are reached.
By feeding the lubricating oil directly back to the oil pump, the oil in the lubricating system heats up more quickly. Moreover, the pressure loss of the lubricating system to be overcome is reduced since the oil flowing back through the bypass line does not flow through the oil sump. Since preferably the oil of the bypass line is conducted through the cylinder block and/or the cylinder head, an increased oil volume flow can be achieved at lower temperatures by at least partially opening the bypass valve, which may be disposed on the cylinder head or the cylinder block. Thus, the oil is able to absorb more heat.
Reduced friction is achieved in the warm-up phase through this measure, since the lubricating oil is brought more quickly up to the operating temperature, and pressure losses are reduced.
The method for heating the lubricating system according to an aspect of the invention can be employed advantageously not only in motor vehicles with automatic transmissions but also in motor vehicles with manual transmissions, and can be used for the lubrication of the combustion engine as well as the transmission. In hybrid vehicles, which comprise a combustion engine as well as an electric drive, this heating method can be used to heat up the motor/generator unit more quickly, which achieve their optimal efficiency only at higher temperatures, and it can also lubricate the components that are driven by the electric motor. In these instances, it is advantageous to utilise the waste heat of the electric energy storage unit (battery) and/or the inverter to heat up the oil in the bypass line, which then heat up the motor/generator unit and may provide better lubrication for said motor/generator unit and a downstream transmission. As with combustion engines, an oil bypass line may also be disposed in automatic transmissions, comprising a heat exchanger through which additional heat is introduced into the transmission oil in the warm-up phase to reduce friction.
The invention can be applied to all types of plants and vehicles powered by combustion engines, such as passenger vehicles, trucks, buses, motorcycles, construction plants, ships, boats, aeroplanes as well as mobile and stationary equipment and devices, energy generating plants, such as emergency generators and similar. In particular in short-term use and under varying workloads the invention enables optimal lubrication to reduce friction between the moving parts so that the longevity of the machine can be increased, the noise level can be reduced, higher efficiency can be achieved, greater power output can be gained, a reduced level of exhaust gases is emitted and costs can be reduced.
Within the framework of the invention it is advantageous if the length of the oil line of the lubricating system from the discharge port of the oil pump up to the joining of the oil bypass line makes up at least 80% of the maximum length of the oil line of the lubricating system from the discharge port of the oil pump to the most distant device to be lubricated. This allows the lubricating oil flowing through the oil bypass line to heat up more quickly. In this context, it is of particular advantage if the lubricating oil mass flow through the oil bypass line is at least sometimes greater than the lubricating oil mass flow through the oil suction pipe and the oil sump. In this instance, the total math flow through the lubricating system is heated up more quickly than without oil bypass line.
Furthermore, it is also expedient if the oil bypass line is disposed inside the same housing in which also at least one of the devices to be lubricated is located so that the returning lubricating oil can be heated up even more. It is particularly advantageous if one or more oil return lines are connected directly to the suction pipe of an oil pump.
It is also advantageous within the meaning of the invention if the oil bypass line consists of or comprises a heat insulating material that has a thermal conductivity coefficient of less than 1 W/(m*K) to reduce the heat transfer to its surroundings during the return flow. This applies particularly to locations where the oil bypass line is not routed through the device to be lubricated.
To further speed up the heating up of the oil and to further reduce the pressure loss of the lubricating system it is advantageous if at least one of the lubricating oil return lines disposed downstream of the devices to be lubricated is connected to the oil bypass line, wherein one of the lubricating oil return lines connected to the oil bypass line is part of an exhaust gas turbocharger.
Since varying lubricating oil pressures are required for different loads and numbers of revolutions to provide adequate lubrication and to prevent damage to the components to be lubricated. According to the invention it is advantageous if the bypass valve in the oil bypass line is closed as soon as a predetermined number of revolutions or speed or torque or force of the components to be lubricated exceeds a preset threshold value.
In an advantageous embodiment of the invention the lubricating oil flowing through the oil bypass line is heated up by a heat exchanger. To accelerate the heating up of the lubricating oil even further it is advantageous if the heat exchanger for heating up the lubricating oil is subjected to the exhaust gas of a combustion engine downstream of a catalytic converter. Here, the exhaust gas flowing through the heat exchanger flows upstream through a valve. This valve is closed as soon as a preset temperature limit of the exhaust gas is reached to prevent coking of the lubricating oil in the heat exchanger.
In order to reduce the combustion temperature and thus also the nitrogen oxide emissions of the combustion engine, the exhaust gas flowing through the heat exchanger within the meaning of the invention advantageously flows as an exhaust gas return downstream through a valve into the intake manifold of a combustion engine, wherein the valve is at least partially closed as soon as a preset exhaust gas temperature limit is reached or as soon as a preset volume flow of the exhaust gas return is reached. During this process, the exhaust gas is cooled off by the heat exchanger, which causes a further reduction in combustion temperature. Hence no additional cooler for the exhaust gas return is required.
According to the invention it is expedient if the exhaust gas of the combustion engine, which flows parallel to the heat exchanger, flows through a further valve and that this valve is sometimes at least partially closed to increase the exhaust gas flow and thus also the heat exchange in the heat exchanger.
In a further advantageous embodiment of the invention a further heat exchanger and a further valve are disposed downstream of the oil pump for cooling, wherein said valve is at least partially opened if a preset threshold value for the lubricating oil temperature is exceeded or underrun. To achieve this, one embodiment uses a cooling medium, such as ambient air or a coolant, flowing through the heat exchanger to cool the lubricating oil. In another embodiment exhaust gas from the combustion engine flows through the heat exchanger to heat up the lubricating oil and reduce friction. It is advantageous if a further valve is disposed in the lubricating oil line parallel to the heat exchanger and the valve. This valve is at least partially closed if a preset threshold value for the lubricating oil temperature is either exceeded or underrun. It is also expedient if this heat exchanger is disposed in the passenger room heating circuit or in the circuit for heating or cooling of an electric battery.
According to the invention it is advantageous for controlling oil pressure and oil temperature if a control unit regulates the opening cross-section of the various valves, and if sensors for detecting lubricating oil pressure, lubricating oil temperature, exhaust gas temperature, number of rotations, load and/or coolant temperature are connected to the control unit.
In an advantageous embodiment of the invention the lubricating system, the exhaust gas line and the intake manifold are part of a combustion engine.
According to the invention it is also advantageous if at least one part of the lubricating system is disposed in a transmission, which is connected to the combustion engine, and if the combustion engine and the transmission are part of the motor vehicle. Here, it is particularly advantageous if the exhaust gas heat exchanger is a double-pipe unit so that the transmission oil and the engine oil can simultaneously be heated up, and that the exhaust gas heat exchanger is connected to the exhaust gas line through a heat-insulating material that has a thermal conductivity coefficient of less than 1 W(m*K).
The sealing of the valves in the exhaust gas line is of particular importance, since a tight seal not only increases the heating effectiveness but also prevents, in the closed position, that the oil is heated up unintentionally, for example at high engine loads and high numbers of rotation (rpm). This makes the application of an additional oil cooler redundant. According to the invention it is thus advantageous if the valves in the exhaust gas line are designed as a single-piece three-way valve and that said valves take the form of double-sided acting poppet valves, wherein the poppet has two sealing surfaces. One of the sealing surfaces is disposed at the outer end of the valve, like on an exhaust valve in the cylinder head of a combustion engine. The second sealing surface is disposed on the opposite side of the poppet, the side from which the valve stem extends to the actuating device. In its activated state, the outer end of the valve shuts off the exhaust bypass, and in the deactivated state, the inner sealing surface of the poppet shuts off the line to the heat exchanger.
In the different Figures the same components are always depicted with the same reference numerals. Hence they are usually described only once.